An electrostatic chuck is used as a means for suction holding an object to be clamped (such as a semiconductor wafer and glass substrate) in substrate processing apparatuses for performing etching, CVD (chemical vapor deposition), sputtering, ion implantation, ashing, light exposure, inspection and the like.
Here, particles may be generated if the mounting surface of the electrostatic chuck and the clamped object rub against each other. Furthermore, the clamping/declamping response of the clamped object may be degraded if the contact area between the mounting surface of the electrostatic chuck and the clamped object is large.
Thus, techniques are known for providing protrusions on the mounting surface side of the electrostatic chuck to decrease the contact area, thereby suppressing particle contamination and improving the clamping/declamping response of the clamped object.
On the other hand, there is known an electrostatic chuck device based on application of polyphase AC voltage so that no electrostatic elimination treatment is needed to declamp the clamped substrate and that there is no vibration of the clamped substrate (Patent Literature 1). However, in the electrostatic chuck device described in Patent Literature 1, AC voltage is applied between the polyphase electrode and the clamped substrate. Thus, there is an instant when the voltage between one of the polyphase electrodes and the clamped substrate becomes zero. Accordingly, the clamping force locally becomes zero in the portion of the clamped substrate located on the electrode applied with zero voltage. The original investigation by the inventor has revealed that this may cause local vibration of the clamped substrate or local rubbing between the clamped substrate and the mounting surface of the electrostatic chuck device.
Accordingly, in the case where protrusions are provided on the mounting surface side of the electrostatic chuck, the protrusion and the clamped substrate may locally rub against each other and cause local damage to part of the protrusions.